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KINETIC MOLECULAR MODEL
AND INTERMOLECULAR FORCES
Kinetic Molecular Model of
Liquids and Solids
Recalling the concept:
Matter in the liquid state has indefinite
shape and definite volume.
Matter in the gas state has indefinite shape
and volume.
Matter in the solid state has definite shape
and volume.
Recalling the concept:
SOLID
ARRANGEMENT OF PARTICLES
-closely and orderly packed
KINETIC ENERGY OF PARTICLES
-vibrate and rotate about a fixed
position
PARTICLE MOTION
-very low
ATTRACTIVE FORCES
-very strong
Recalling the concept:
LIQUID
ARRANGEMENT OF PARTICLES
-less closely packed
KINETIC ENERGY OF PARTICLES
-particles slide over each other
PARTICLE MOTION
-low
ATTRACTIVE FORCES
-strong
Recalling the concept:
GAS
ARRANGEMENT OF PARTICLES
-very far apart
KINETIC ENERGY OF PARTICLES
-particles move at great speed
PARTICLE MOTION
-high
ATTRACTIVE FORCES
-low
Polar attraction as a universal law…
 Molecules are held together by an
electrostatic attraction:
a. Intramolecular attraction
IONIC COVALENT
METALLIC
Polar attraction as a universal law…
 Molecules are held together by an
electrostatic attraction:
a. Intermolecular forces
van der Waals forces:
 The term for all known Intermolecular
forces.
 Named after a Dutch scientist:
Johannes van der Waals (1837 –
1932)
Types of van der Waals forces:
Ion – dipole
 Results when an ion and the partial charge
found at the end of the polar molecule attract
each other.
 Positive ions are attracted to the negative
end of a dipole and vice versa.
Example:
a. Salt (NaCl) Dissolved in Water (H2O)
b. Potassim (K+) Dissolved in Hydrochloric
Acid (HCl)
Types of van der Waals forces:
Ion – dipole
 Results when an ion and the partial charge
found at the end of the polar molecule attract
each other.
Example:
a. Salt (NaCl) Dissolved in Water (H2O)
b. Potassim (K+) Dissolved in Hydrochloric
Acid (HCl)
Types of van der Waals forces:
Dipole – dipole
 Exists between neutral polar molecules
 Polar molecules attract each other when the
positive end of one molecule is near the
negative end of another.
 Weaker force compared to ion-dipole
(depending on size)
Types of van der Waals forces:
Dipole – dipole
Example:
a. Dichloromethane
b. Hydrochloric Acid
Types of van der Waals forces:
London Dispersion Forces
 Force of attraction between nonpolar
molecules or atoms (Cl2 and CH4)
 Originated from Fritz London (1900-1954), a
German-American physicist
Types of van der Waals forces:
London Dispersion Forces
Instantaneous
dipole
Induced
dipoles
Types of van der Waals forces:
London Dispersion Forces
 Dipole can be induced more likely on
molecules having larger molecular masses.
(Polarizability)
-This also affects the melting and boiling
points of the molecules.
Types of van der Waals forces:
Hydrogen Bonds
 Plays an important role in life
processes
 It can easily be broken and reformed
 Occurs in water, DNA molecules and
protein
Types of van der Waals forces:
Hydrogen Bonds
 It is an attractive interaction between a
hydrogen atom bonded to an electronegative
Fluorine, Oxygen and Nitrogen atom and an
unshared electron pair of another nearby
electronegative atom.
Types of van der Waals forces:
Hydrogen Bonds
Example:
a. Water (H2O)
b. Ammonia
c. Ammonia and Water (NH3)
d. Hydrofluoric Acid (HF)
PROPERTIES OF LIQUIDS
What factors determine the physical
properties of liquids?
POPERTIES OF LIQUIDS
A. VISCOSITY
 What is the difference between fluid
and viscous liquids?
 VISCOSITY is the ability of a fluid to
resist flowing.
 Viscosity of a
liquid depends on
intermolecular
forces that is
present.
POPERTIES OF LIQUIDS
A. VISCOSITY
 Non-polar molecules have low
viscosities because of weak London
Force. Example: Benzene, pentane and
carbon tetrachloride.
 Polar molecules
such as glycerol
and aqueous
sugar solution
have high
viscosities.
POPERTIES OF LIQUIDS
A. VISCOSITY
What do you think is the effect of an
increasing temperature to the viscosity of
a liquid?
The
viscosity
decreases
as the
Types of van der Waals forces:
A. VISCOSITY
 VISCOMETER is a device used to
measure viscosity.
POPERTIES OF LIQUIDS
B. SURFACE TENSION
POPERTIES OF LIQUIDS
B. SURFACE TENSION
 The measure of the resistance of a
liquid to spread out.
 The higher the
temperature, the
less the strength
of the attractive
force that holds
the molecule
together
POPERTIES OF LIQUIDS
C. CAPILLARITY
 The rising of any liquid
 Results from
competition between
liquid’s intermolecular
force and the walls of
the tube.
 Capillarity is also
observed in plants’
transport system.
POPERTIES OF LIQUIDS
POPERTIES OF LIQUIDS
D. EVAPORATION, VAPOR
PRESSURE AND BOILING POINT
 Molecules of liquids, when obtained
enough kinetic energy liberates
 The escape of energetic molecules
in liquid reduces the average kinetic
energy of the remaining molecules
POPERTIES OF LIQUIDS
D. EVAPORATION, VAPOR
PRESSURE AND BOILING POINT
POPERTIES OF LIQUIDS
D. EVAPORATION, VAPOR
PRESSURE AND BOILING POINT
 What do you think is the relationship of
liquid evaporation to temperature and
pressure?
 The escape of energetic molecules
in liquid reduces the average kinetic
energy of the remaining molecules
POPERTIES OF LIQUIDS
D. EVAPORATION, VAPOR
PRESSURE AND BOILING POINT
Dynamic
Equilibrium
Vaporization Condensation
POPERTIES OF LIQUIDS
ANALYSIS
 Normal boiling point happens when a
liquid reaches an internal temperature
of 100OC under
1 atm (atmospheric pressure)
Which level with respect to sea
level foods cooks faster and
slower?
POPERTIES OF LIQUIDS
At higher altitude,
atmospheric pressure is
lesser.
Thus water boils faster at a
lower temperature because
less pressure is exerted on
water molecules.
Inefficient delivery of heat to
cook the food and it takes time
for the food to be cooked.
Lets check your
understanding.
Answer the following questions briefly in a ½ sheet of
pad paper; copy and answer.
1. Why do droplets of water come in spherical
shape on top of the leaves of the plants like
gabi?
2. Boiling points varies with location.
3. Your arm feels cool when alcohol
evaporates from your skin.
4. On a warm day, water droplets form on the
outside of the bottle of a carbonated
beverage.
PROPERTIES OF SOLIDS
How are the structures and properties of
solids related?
POPERTIES OF SOLIDS
 A SOLID is formed when
the temperature of a
liquid is low and the
pressure is sufficiently
high causing the
particles to come very
close to one another.
 They are rigid
 Their particles hardly
diffuse
POPERTIES OF SOLIDS
NATURE OF SOLIDS
Crystalline
Solids
Amorphous
Solids
POPERTIES OF SOLIDS
A. CRYSTALLINE
 Atoms, ions, or molecules are arranged
in well defined arrangement
 Having flat surface and sharp edges
 Example: gems, salts, sugar and ice.
POPERTIES OF SOLIDS
TYPES OF CRYSTALLINE SOLIDS
Ionic
Molecular
Covalent Network
Metallic
POPERTIES OF SOLIDS
1. Ionic Crystalline Solids
 Composed of (+) and (-) ions
 Held by electrostatic attractions
 They are hard, brittle and poor
electrical and thermal conduction
 Example: NaCl
POPERTIES OF SOLIDS
2. Molecular Crystalline Solids
 Composed of atoms and molecules
 Held together by: H-Bond, dipole-
dipole, and London dispersion forces
 Soft, low to moderate melting point and
poor thermal and electrical
conductivity
 Examples: CH4, C12H22O11, CO2, H2O
and Br2
POPERTIES OF SOLIDS
3. Covalent Network Crystalline
Solids
 Atoms connected in a network of
covalent molecules
 Held together by covalent bonds
 Very hard, very high melting point and
often poor thermal and electrical
conductivity.
 Examples: Plastics, Allotropes of
carbon, silicon carbide
POPERTIES OF SOLIDS
4. Metallic Crystalline Solids
 Composed of atoms and molecules
 Held together by metallic bonds
 Soft to hard, low to high melting point,
malleable, ductile and good thermal
and electrical conduction
 All metallic elements: Cu, Na, Zn, Fe
and Al
POPERTIES OF SOLIDS
How are molecules being
arranged in microscopic level?
Unit Cell
Crystal
Lattice
The smallest portion of the
crystal which shows the
complete pattern of its
particles
The repetition of unit cells
in all directions
POPERTIES OF SOLIDS
Structural
Representations
of Molecules:
1. NaCl
2. Ice
3. Diamond
4. Metallic Bond
in (Fe)
POPERTIES OF SOLIDS
B. AMORPHOUS SOLIDS
 From the Greek word for “without
form”
 Solid particles which do not have
orderly structures.
 They have poorly defined shapes
 are rigid, but they lack repeated
periodicity or long-range order in their
structure.
 examples include thin film lubricants,
metallic glasses, polymers, and gels
POPERTIES OF SOLIDS
STRUCTURE OF AMORPHOUS SOLID:
POPERTIES OF SOLIDS
CRYSTALLINE VERSUS AMORPHOUS SOLIDS
POPERTIES OF SOLIDS
 It can be noted that as temperature of
crystalline solid is increased, the
particles vibrate back and forth about
its lattice point.
 The crystal becomes less ordered.
 The heat added increases the kinetic
motion of the particles.
 Until the crystalline structure is
completely destroyed by the vibrations
of the particles, melting is achieved.
POPERTIES OF LIQUIDS
ANALYSIS
 What will happen if heating stops and
no heat is allowed to escape?
Both solid and liquid phases are
present in equilibrium.
PHASE CHANGE
Heating curve for the conversion of ice to
gaseous water.
PHASE CHANGE
ANALYSIS
 How does intermolecular force relates
to the rate at which melting point of a
substance is achieved?
Forces of attraction are weak in
substances with lower melting
point and vice versa.
PHASE CHANGE
VOCABULARIES
 HEAT FUSION- refers to the amount of
energy required to overcome the
intermolecular forces to convert a solid
into a liquid
 HEAT VAPORIZATION- the amount of
energy required to convert a liquid into
a gas.
PHASE CHANGE
SYNTHESIS
 Ionic Compounds have very high
melting point because of a very strong
intermolecular force.
 Example:
 NaCl
 MgCl2
 BeF
 CaF2
PHASE CHANGE
SYNTHESIS
 Covalent compounds have low to
moderate melting point because of
weak intermolecular force.
 Example:
 Water
 Glycerin
 Hormones
 Other Fats
QUANTITATIVE ASPECTS IN PHASE
CHANGES
 Different substances absorbs heat in
varying amounts.
 SPECEFIC HEAT is defined as the amount
of heat needed to raise the temperature of
one gram of substance by one degree
Celsius.
Q = mc T
Q= heat
m= mass
c= specific heat capacity
T= change in temperature
QUANTITATIVE ASPECTS IN PHASE
CHANGES
NOTE:
 When materials with small specific heat
value absorbs energy, its temperature rises
rapidly.
 In contrast, materials with high specific heat
values absorb a large amount of heat
without much increase in temperature.
 Water has a specific heat capacity of 4.16
Joules.
QUANTITATIVE ASPECTS IN PHASE
CHANGES
SAMPLE PROBLEM:
 Hot water at 100oC can burn and damage
the skin, but the effect of steam on the skin
can be even more severe. Calculate the
amount of heat absorbed by the skin from a
150-g steam burned at 100oC.
ENERGY CHANGES IN
CHEMICAL REACTIONS
Thermochemistry
THERMOCHEMISTRY
INTRODUCTION
Energy is the foundation of the
universe.
THERMOCHEMISTRY
 Energy transfer may be in the form of
heat or work.
 HEAT (Q) – is the transfer or energy
between a system and surroundings
due to temperature difference.
 Heat may be absorbed or released by a
system depending on which has a
higher temperature between the
system and the surroundings.
THERMOCHEMISTRY
 During chemical reaction, there is an
energy change between molecules.
 TWO TYPES OF REACTIONS:
Endothermic
Exothermic
THERMOCHEMISTRY
THERMOCHEMISTRY
 The study of energy changes that
occur during chemical reactions and
changes of state.
THERMOCHEMISTRY
ANALYSIS
 How does energy undergo change
within a system or within a chemical
reaction?
Heat flows in and out of the
system during chemical reactions.
THERMOCHEMISTRY
THE LAW OF CONSERVATION OF
ENERGY:
 In any chemical or physical process,
energy is neither created nor
destroyed.
 In any chemical or physical process,
energy in the universe remains
unchanged.
Energyuniv = constant
THERMOCHEMISTRY
Recitation: Explain how energy is
conserved in the following situations:
 Burning of gasoline
 Hydroelectric powerplant
 Cellphone telecommunications
 Condensation of water vapor
 Induction cooking
THERMOCHEMISTRY
THREE TYPES OF SYSTEMS:
Open System
Closed System
Isolated System
THERMOCHEMISTRY
OPEN SYSTEM
 Matter and energy occurs between
system and surrounding
 System interacts with the surrounding
THERMOCHEMISTRY
CLOSED SYSTEM
 Only energy can transfer between
system and surroundings
ISOLATED SYSTEM
 Matter and energy cannot transfer
between the system and its
surroundings.
 Example: contents of adiabatic bomb
calorimeter.
THERMOCHEMISTRY
The magnitude of heat can be computed
using the following equation
Q = mc T
Q= heat
m= mass
c= specific heat capacity
T= change in temperature
THERMOCHEMISTRY
WORK (w)
 Force applied over a given distance
 Energy transfer between a system and
the surrounding due to a force acting
through a distance
THERMOCHEMISTRY
TABLE 3.2: Assigned Convention for Work, w
System does work
on the
surroundings
-w Expansion
Surroundings does
work on the system +w Compression
THERMOCHEMISTRY
SAMPLE PROBLEM:
 How much work is needed in a system
to expand from 25 to 50 liters against a
pressure of 5 atm? Is work done by the
system or on the system?
THERMOCHEMISTRY
SAMPLE PROBLEM:
 How much work is needed in a
system to compress a carbon
dioxide gas inside a fire
extinguisher from the volume of
500 liter to 275 liter at 3.5 atm? Is
work done by the system or on the
sytem?
THERMOCHEMISTRY
ENTHALPY
 In a chemical reaction, there is an
energy change from the beginning up
to the end of the reaction.
 Change in energy: ENDOTHERMIC OR
EXOTHERMIC REACTION
 Represented by H
THERMOCHEMISTRY
ENTHALPY
 Energy change in the reaction or the
sum of all the energy stored in the
bonds of the product minus the energy
stored in the bond of the reactant
 If there is more energy in the product
than the reactant, the value of H is
positive = ENDOTHERMIC REACTION
THERMOCHEMISTRY
THERMOCHEMICAL EQUATIONS
 If there is less energy in the product than
the reactant, the value of H is
negative = EXOTHERMIC REACTION
THERMOCHEMISTRY
WRITING THERMOCHEMICAL
EQUATIONS:
I. When heat is lost, the H value is
negative. (Exothermic reaction)
CH4(g) + 2O2 ------ CO2(g) + 2H2O(l)
H = -890 kJ
THERMOCHEMISTRY
WRITING THERMOCHEMICAL
EQUATIONS:
I. When heat is gained, the H value is
positive. (Endothermic reaction)
CO2(g) + 2H2O(l) ------ CH4(g) + 2O2
H = 890 kJ
THERMOCHEMISTRY
WRITING THERMOCHEMICAL
EQUATIONS:
II. HEAT IS A STATE FUNCTION, thus
energy changes or H value for the same
equation may be different if it occurs in
different physical state.
THERMOCHEMISTRY
WRITING THERMOCHEMICAL
EQUATIONS:
III. If a reaction is reversed, then the
enthalpy H value will also be reversed.
Hence +a becomes –a and vice versa
THERMOCHEMISTRY
WRITING THERMOCHEMICAL
EQUATIONS:
III. If we change the stoichiometric
coefficients in the reaction, we also
change the enthalpy H value
proportionally!
THERMOCHEMISTRY
WRITING THERMOCHEMICAL
EQUATIONS:
a. If coefficient is doubled enthalpy must be
doubled also
b. If we triple the coefficient, enthalpy must
also be tripled
c. Same with when we half the coefficient.
d. If we double the equation and reverse, we
must also double the enthalpy and
reverse the sign
THERMOCHEMISTRY
Sample Problem:
a. Manipulate the thermochemical equation
below as endothermic reaction:
CH4(g) + 2O2 ------ CO2(g) + 2H2O(l)
H = -890 kJ
THERMOCHEMISTRY
HESS LAW
 States that the enthalpy change of an overall
reaction is the sum of the enthalpy changes
of its individual steps.
EXAMPLE: we can burn carbon directly to
carbon dioxide
C(s) + O2(g) ------------ CO2(g) H= -393.509 kJ
OR
THERMOCHEMISTRY
HESS LAW
 Carbon to carbon monoxide, then carbon
monoxide to carbon dioxide
C(s) + ½ O2(g) ----------- CO(G) H= -110.524 kJ
CO(g) + ½ O2(g) --------- CO2(g) H= -282.958 kJ
____________________________________________
C(s) + O2(g) ------------- CO2(g) H= -393.509 kJ
THERMOCHEMISTRY
STEPS IN GETTING THE HEAT
SUMMATION:
1. Identify the net equation whose ∆H is
unknown. Make sure that the reaction is
balanced.
2. Manipulate the equations where ∆H is
known so that the correct moles of the
reactants and the products are on correct
sides.
THERMOCHEMISTRY
STEPS IN GETTING THE HEAT
SUMMATION:
1. Add these individual reactions to get the net
reaction. The value of the unknown ∆H is the
sum of the individual manipulated ∆H.
THERMOCHEMISTRY
STEPS IN GETTING THE HEAT
SUMMATION:
1. Add these individual reactions to get the net
reaction. The value of the unknown ∆H is the
sum of the individual manipulated ∆H.
REACTION RATES
Chemical Kinetics
Chemical Kinetics
Reaction Rate
 How fast the reaction takes place
 Some reactions proceed at very fast rate
while others proceed very slowly
 Fractions of the reactants are changed into
product until all the substances are
converted fully.
(R)Rate= M(molar mass)/s(second)
Examples of Reaction
 Burning of Rocket Fuel
 Spoiling of food outside the refrigerator
 Rusting of Iron
Chemical Kinetics
Factors Affecting Rates of Reactions
A. Nature of Reactants:
 Reaction depends on the particular
reactants and the number of bonds that
have to be broken.
 Reactions are rapid between oppositely-
charged particles
 Reactions involving covalent substances
are slow at room temperature.
 Gasses proceed quick reactions than solid
and liquid.
 The reactions between heterogeneous
reactions are slower than homogeneous
reactions
Factors Affecting Rates of Reactions
B. Concentration:
 An increase in concentration of the reactant
indirectly means an increase in collision
theory, thus increasing the reaction rate.
Factors Affecting Rates of Reactions
C. Surface Area:
 The smaller the size of particles, the larger
the surface area exposed.
A larger surface area increases the frequency
of collisions
Factors Affecting Rates of Reactions
C. Effects of Catalyst:
 Provides an alternative pathway of lower
activation energy.
 Representation of a chemical equation with
the presence of catalyst:
2H2O2 → O2 + 2H2O
MnO4
Factors Affecting Rates of Reactions
C. Effects of Temperature
 Food spoilage at room temperature on warm
summer days
 Most plants grow faster in warm than in cold
weather.
 Animals living at moderate pressure under
the deep sea are fatty than those fishes
living in the shallow portion of the
sea/freshwater.
Identify the factors that influence
reaction rates and explain:
1. A brush (grass fire) spreads more rapidly
on a sunny day than on an overcast day.
2. Sodium reacts more rapidly with water than
iron does.
3. Powdered zinc reacts more rapidly with
sulfuric acid than a large piece of zinc of
equal weight does.
4. It is more dangerous to drop a lighted
match into a gasoline tank that has just
been emptied than into one which is
completely full.
5. Cake batter will cook only when heated.
QUIZ
Identify the factors that influence reaction
rates and explain:
PROGRESS OF
CHEMICAL REACTION
Chemical Reaction
THERMOCHEMISTRY
RATE LAW
 The concentration of reactants influences
the rate of chemical reactions.
 The effect of concentration of reactants on
the rate of reaction can be seen
quantitatively using the rate law for the
reaction.
 An expression that gives a mathematical
relationship of the rate of a reaction and the
concentration of reactants.
Rate= k[A]m[B]n
THERMOCHEMISTRY
Consider the equation between oxygen
and nitric oxide in the formation of acid
rain:
O2(g) + 2NO(g) → 2NO2(g)
Rate= k[O2]m[NO]n
THERMOCHEMISTRY
Rate= k[O2]m[NO]n
 Brackets represent the concentration of the
reactants given in moles per liter
 k= the fixed value for rate constant
 m and n represent the order of the reaction
 In getting the experimental value for m and
n, the concentration of one of the reactants
is changed while the other is kept constant.
THERMOCHEMISTRY
 Doubling the
initial
concentration
of the
reactants, the
rate of the
reaction is also
doubled
The reaction is FIRST ORDER
WITH RESPECT TO N2O5
THERMOCHEMISTRY
THERMOCHEMISTRY
THERMOCHEMISTRY
Example Problem:
R= k[O2][NO]2
THERMOCHEMISTRY
R= k[O2][NO]2
0.04M/s=k(0.250M)(0.100M)
k= 1.6 M/s
Rate of Chemical Reaction
The following data were obtained for the
reaction:
A2 + B2 +3C → D
Experiment
No.
Reactant Concentrations Rate of
Reaction
(M/s)
[A] [B] [C]
1 0.10 0.20 0.20 0.0090
2 0.20 0.20 0.30 0.0360
3 0.20 0.60 0.30 0.0720
4 0.20 0.20 0.60 0.2880
BALANCING REDOX REACTIONS
Review:
 Electrons makes it possible for one atom
bind with another atom.
 In acid-base reactions, transfer of proton
(H+) is involved.
BALANCING REDOX REACTIONS
What is a REDOX reaction?
 RED(Reduction): Substance gain an
electron
 Antoine Lavosier may leave or goes in into a
substance, thus changing its mass.
 OX(Oxidation): Tendency of a substance to
loose an electron.
BALANCING REDOX REACTIONS
REDOX IN NATURE:
 Cellular Respiration
 Photosynthesis
 Battery charging
 Burning process
BALANCING REDOX REACTIONS
In electron transfer,
 We track electrons like a banking
transactions.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Fe(s) + Cu2+
(aq) + SO4
2-
(aq) → Fe2+
(aq) + SO4
2-
(aq) + Cu(s)
Fe(s) + Cu2+
(aq) → Fe2+
(aq) + Cu(s)
Lost of e- (oxidized)
Gain of e- (reduced)
Reducing Agent
Oxidizing Agent
BALANCING REDOX REACTIONS
Oxidation number in tracking electrons:
 Hypothetical value for each atom in a
molecule (not actual)
 ELEMENT: zero (0) oxidation# (He, O2, Fe)
 MONOATOMIC ION: the same with its ionic
charge (Oxygen -2, Fe +2)
 NEUTRAL MOLECULE: ox. Numbers add up
to get zero [CO2 (+4 -4)]
BALANCING REDOX REACTIONS
Assigning Oxidation Number:
4Fe(s) + 3O2 → 2Fe2O3
0 0 +3 -2
Fe: 0 → +3: Loss of –e [oxidized]
O: 0 → -2: Gain of –e [reduced] Oxidizing Agent
Reducing Agent
BALANCING REDOX REACTIONS
Practice
PbO2
MnO4
S
NH3
BALANCING REDOX REACTIONS
Balancing a Redox Reaction
0 0 +3 -2
Fe: 0 → +3: Loss of –e [oxidized]
O: 0 → -2: Gain of –e [reduced] Oxidizing Agent
Reducing Agent
BALANCING REDOX REACTIONS
Consider the aqueous solution iron (II) ion (Fe3+) with
dichromate ion (Cr2O7
-2):
4Fe2+ + Cr2O7
-2 → 4Fe3+ Cr3+
STEPS:
Separate the unbalanced reaction into half-reactions. A half
reaction is an oxidation/reduction that occurs as part of
overall redox reaction.
Oxidation: Fe2+ → Fe3+
Reduction: Cr2O7
-2 → Cr3+
BALANCING REDOX REACTIONS
4Fe2+ + Cr2O7
-2 → 4Fe3+ Cr3+
STEPS:
Balance each of the half-reactions with regard to atoms other
than O and H. In this case, no change is required for the
oxidation half-reaction. We adjust the coefficient of the
chromium (III) ion to balance the reduction half reaction.
Oxidation: Fe2+ → Fe3+
Reduction: Cr2O7
-2 → 2Cr3+
BALANCING REDOX REACTIONS
4Fe2+ + Cr2O7
-2 → 4Fe3+ Cr3+
STEPS:
Balance both half-reactions for H by adding H+ . Once again,
the oxidation in this case requires no change, but we must add
14 hydrogen ions to the product side of the reaction.
Oxidation: Fe2+ → Fe3+
Reduction: Cr2O7
-2 → 2Cr3+ + 7H2O
BALANCING REDOX REACTIONS
4Fe2+ + Cr2O7
-2 → 4Fe3+ Cr3+
STEPS:
Balance both half-reactions for H by adding H+ Once again,
the oxidation in this case requires no change but we must add
14 hydrogen ions to the reactant side of the reaction
Oxidation: Fe2+ → Fe3+
Reduction: 14H+ + Cr2O7
-2 → 2Cr3+ + 7H2O
BALANCING REDOX REACTIONS
4Fe2+ + Cr2O7
-2 → 4Fe3+ Cr3+
STEPS:
Balance both half-reactions for charge by adding electrons. To
do this, we determine the total charge on each side and add
electrons to make total charges equal.
Oxidation: Fe2+ → Fe3+ + e-
+2 +2
BALANCING REDOX REACTIONS
4Fe2+ + Cr2O7
-2 → 4Fe3+ Cr3+
STEPS:
In case of reduction, there is total charge of
[(14)(+1) + (2)(-)] = +12 on the reactant side and a total charge
of [(2)(+3)] = +6 on the product side. Adding six electrons to
the reactant side makes the charges equal
Reduction: + 14H+ + Cr2O7
-2 → 2Cr3+ + 7H2O
+6 +6
6e-
BALANCING REDOX REACTIONS
4Fe2+ + Cr2O7
-2 → 4Fe3+ Cr3+
STEPS:
If the number of electrons in the balanced oxidation half-reaction
is not the same as the number of electrons in the balanced
reduction half-reaction, multiply one or both of the half-reactions
by the number(s) req. to make it balanced.
Oxidation: 6(Fe2+ → Fe3+ e-)
6Fe2+ → 6Fe3+ 6e-
Reduction: 6e- +14H+ + Cr2O7
-2 → 2Cr3+ + 7H2O
BALANCING REDOX REACTIONS
4Fe2+ + Cr2O7
-2 → 4Fe3+ Cr3+
STEPS:
Finally, add the balanced half-reactions back together and cancel
the electrons, in addition to any other identical terms that appear
on both sides.
6Fe2+ → 6Fe3+ 6e-
6e- +14H+ + Cr2O7
-2 → 2Cr3+ + 7H2O
6Fe2++14H+ + Cr2O7
-2 → 6Fe3+ + 2Cr3+ + 7H2O

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KINETIC MOLECULAR MODEL AND INTERMOLECULAR FORCES

  • 1. KINETIC MOLECULAR MODEL AND INTERMOLECULAR FORCES Kinetic Molecular Model of Liquids and Solids
  • 2. Recalling the concept: Matter in the liquid state has indefinite shape and definite volume. Matter in the gas state has indefinite shape and volume. Matter in the solid state has definite shape and volume.
  • 3. Recalling the concept: SOLID ARRANGEMENT OF PARTICLES -closely and orderly packed KINETIC ENERGY OF PARTICLES -vibrate and rotate about a fixed position PARTICLE MOTION -very low ATTRACTIVE FORCES -very strong
  • 4. Recalling the concept: LIQUID ARRANGEMENT OF PARTICLES -less closely packed KINETIC ENERGY OF PARTICLES -particles slide over each other PARTICLE MOTION -low ATTRACTIVE FORCES -strong
  • 5. Recalling the concept: GAS ARRANGEMENT OF PARTICLES -very far apart KINETIC ENERGY OF PARTICLES -particles move at great speed PARTICLE MOTION -high ATTRACTIVE FORCES -low
  • 6. Polar attraction as a universal law…  Molecules are held together by an electrostatic attraction: a. Intramolecular attraction IONIC COVALENT METALLIC
  • 7. Polar attraction as a universal law…  Molecules are held together by an electrostatic attraction: a. Intermolecular forces
  • 8. van der Waals forces:  The term for all known Intermolecular forces.  Named after a Dutch scientist: Johannes van der Waals (1837 – 1932)
  • 9. Types of van der Waals forces: Ion – dipole  Results when an ion and the partial charge found at the end of the polar molecule attract each other.  Positive ions are attracted to the negative end of a dipole and vice versa. Example: a. Salt (NaCl) Dissolved in Water (H2O) b. Potassim (K+) Dissolved in Hydrochloric Acid (HCl)
  • 10. Types of van der Waals forces: Ion – dipole  Results when an ion and the partial charge found at the end of the polar molecule attract each other. Example: a. Salt (NaCl) Dissolved in Water (H2O) b. Potassim (K+) Dissolved in Hydrochloric Acid (HCl)
  • 11. Types of van der Waals forces: Dipole – dipole  Exists between neutral polar molecules  Polar molecules attract each other when the positive end of one molecule is near the negative end of another.  Weaker force compared to ion-dipole (depending on size)
  • 12. Types of van der Waals forces: Dipole – dipole Example: a. Dichloromethane b. Hydrochloric Acid
  • 13. Types of van der Waals forces: London Dispersion Forces  Force of attraction between nonpolar molecules or atoms (Cl2 and CH4)  Originated from Fritz London (1900-1954), a German-American physicist
  • 14. Types of van der Waals forces: London Dispersion Forces Instantaneous dipole Induced dipoles
  • 15. Types of van der Waals forces: London Dispersion Forces  Dipole can be induced more likely on molecules having larger molecular masses. (Polarizability) -This also affects the melting and boiling points of the molecules.
  • 16. Types of van der Waals forces: Hydrogen Bonds  Plays an important role in life processes  It can easily be broken and reformed  Occurs in water, DNA molecules and protein
  • 17. Types of van der Waals forces: Hydrogen Bonds  It is an attractive interaction between a hydrogen atom bonded to an electronegative Fluorine, Oxygen and Nitrogen atom and an unshared electron pair of another nearby electronegative atom.
  • 18. Types of van der Waals forces: Hydrogen Bonds Example: a. Water (H2O) b. Ammonia c. Ammonia and Water (NH3) d. Hydrofluoric Acid (HF)
  • 19. PROPERTIES OF LIQUIDS What factors determine the physical properties of liquids?
  • 20. POPERTIES OF LIQUIDS A. VISCOSITY  What is the difference between fluid and viscous liquids?  VISCOSITY is the ability of a fluid to resist flowing.  Viscosity of a liquid depends on intermolecular forces that is present.
  • 21. POPERTIES OF LIQUIDS A. VISCOSITY  Non-polar molecules have low viscosities because of weak London Force. Example: Benzene, pentane and carbon tetrachloride.  Polar molecules such as glycerol and aqueous sugar solution have high viscosities.
  • 22. POPERTIES OF LIQUIDS A. VISCOSITY What do you think is the effect of an increasing temperature to the viscosity of a liquid? The viscosity decreases as the
  • 23. Types of van der Waals forces: A. VISCOSITY  VISCOMETER is a device used to measure viscosity.
  • 24.
  • 25. POPERTIES OF LIQUIDS B. SURFACE TENSION
  • 26. POPERTIES OF LIQUIDS B. SURFACE TENSION  The measure of the resistance of a liquid to spread out.  The higher the temperature, the less the strength of the attractive force that holds the molecule together
  • 27. POPERTIES OF LIQUIDS C. CAPILLARITY  The rising of any liquid  Results from competition between liquid’s intermolecular force and the walls of the tube.  Capillarity is also observed in plants’ transport system.
  • 29. POPERTIES OF LIQUIDS D. EVAPORATION, VAPOR PRESSURE AND BOILING POINT  Molecules of liquids, when obtained enough kinetic energy liberates  The escape of energetic molecules in liquid reduces the average kinetic energy of the remaining molecules
  • 30. POPERTIES OF LIQUIDS D. EVAPORATION, VAPOR PRESSURE AND BOILING POINT
  • 31. POPERTIES OF LIQUIDS D. EVAPORATION, VAPOR PRESSURE AND BOILING POINT  What do you think is the relationship of liquid evaporation to temperature and pressure?  The escape of energetic molecules in liquid reduces the average kinetic energy of the remaining molecules
  • 32.
  • 33. POPERTIES OF LIQUIDS D. EVAPORATION, VAPOR PRESSURE AND BOILING POINT Dynamic Equilibrium Vaporization Condensation
  • 34. POPERTIES OF LIQUIDS ANALYSIS  Normal boiling point happens when a liquid reaches an internal temperature of 100OC under 1 atm (atmospheric pressure) Which level with respect to sea level foods cooks faster and slower?
  • 35. POPERTIES OF LIQUIDS At higher altitude, atmospheric pressure is lesser. Thus water boils faster at a lower temperature because less pressure is exerted on water molecules. Inefficient delivery of heat to cook the food and it takes time for the food to be cooked.
  • 36. Lets check your understanding. Answer the following questions briefly in a ½ sheet of pad paper; copy and answer. 1. Why do droplets of water come in spherical shape on top of the leaves of the plants like gabi? 2. Boiling points varies with location. 3. Your arm feels cool when alcohol evaporates from your skin. 4. On a warm day, water droplets form on the outside of the bottle of a carbonated beverage.
  • 37. PROPERTIES OF SOLIDS How are the structures and properties of solids related?
  • 38. POPERTIES OF SOLIDS  A SOLID is formed when the temperature of a liquid is low and the pressure is sufficiently high causing the particles to come very close to one another.  They are rigid  Their particles hardly diffuse
  • 39. POPERTIES OF SOLIDS NATURE OF SOLIDS Crystalline Solids Amorphous Solids
  • 40. POPERTIES OF SOLIDS A. CRYSTALLINE  Atoms, ions, or molecules are arranged in well defined arrangement  Having flat surface and sharp edges  Example: gems, salts, sugar and ice.
  • 41. POPERTIES OF SOLIDS TYPES OF CRYSTALLINE SOLIDS Ionic Molecular Covalent Network Metallic
  • 42. POPERTIES OF SOLIDS 1. Ionic Crystalline Solids  Composed of (+) and (-) ions  Held by electrostatic attractions  They are hard, brittle and poor electrical and thermal conduction  Example: NaCl
  • 43. POPERTIES OF SOLIDS 2. Molecular Crystalline Solids  Composed of atoms and molecules  Held together by: H-Bond, dipole- dipole, and London dispersion forces  Soft, low to moderate melting point and poor thermal and electrical conductivity  Examples: CH4, C12H22O11, CO2, H2O and Br2
  • 44. POPERTIES OF SOLIDS 3. Covalent Network Crystalline Solids  Atoms connected in a network of covalent molecules  Held together by covalent bonds  Very hard, very high melting point and often poor thermal and electrical conductivity.  Examples: Plastics, Allotropes of carbon, silicon carbide
  • 45. POPERTIES OF SOLIDS 4. Metallic Crystalline Solids  Composed of atoms and molecules  Held together by metallic bonds  Soft to hard, low to high melting point, malleable, ductile and good thermal and electrical conduction  All metallic elements: Cu, Na, Zn, Fe and Al
  • 46. POPERTIES OF SOLIDS How are molecules being arranged in microscopic level? Unit Cell Crystal Lattice The smallest portion of the crystal which shows the complete pattern of its particles The repetition of unit cells in all directions
  • 47. POPERTIES OF SOLIDS Structural Representations of Molecules: 1. NaCl 2. Ice 3. Diamond 4. Metallic Bond in (Fe)
  • 48. POPERTIES OF SOLIDS B. AMORPHOUS SOLIDS  From the Greek word for “without form”  Solid particles which do not have orderly structures.  They have poorly defined shapes  are rigid, but they lack repeated periodicity or long-range order in their structure.  examples include thin film lubricants, metallic glasses, polymers, and gels
  • 49. POPERTIES OF SOLIDS STRUCTURE OF AMORPHOUS SOLID:
  • 50. POPERTIES OF SOLIDS CRYSTALLINE VERSUS AMORPHOUS SOLIDS
  • 51. POPERTIES OF SOLIDS  It can be noted that as temperature of crystalline solid is increased, the particles vibrate back and forth about its lattice point.  The crystal becomes less ordered.  The heat added increases the kinetic motion of the particles.  Until the crystalline structure is completely destroyed by the vibrations of the particles, melting is achieved.
  • 52. POPERTIES OF LIQUIDS ANALYSIS  What will happen if heating stops and no heat is allowed to escape? Both solid and liquid phases are present in equilibrium.
  • 53. PHASE CHANGE Heating curve for the conversion of ice to gaseous water.
  • 54. PHASE CHANGE ANALYSIS  How does intermolecular force relates to the rate at which melting point of a substance is achieved? Forces of attraction are weak in substances with lower melting point and vice versa.
  • 55. PHASE CHANGE VOCABULARIES  HEAT FUSION- refers to the amount of energy required to overcome the intermolecular forces to convert a solid into a liquid  HEAT VAPORIZATION- the amount of energy required to convert a liquid into a gas.
  • 56. PHASE CHANGE SYNTHESIS  Ionic Compounds have very high melting point because of a very strong intermolecular force.  Example:  NaCl  MgCl2  BeF  CaF2
  • 57. PHASE CHANGE SYNTHESIS  Covalent compounds have low to moderate melting point because of weak intermolecular force.  Example:  Water  Glycerin  Hormones  Other Fats
  • 58. QUANTITATIVE ASPECTS IN PHASE CHANGES  Different substances absorbs heat in varying amounts.  SPECEFIC HEAT is defined as the amount of heat needed to raise the temperature of one gram of substance by one degree Celsius. Q = mc T Q= heat m= mass c= specific heat capacity T= change in temperature
  • 59. QUANTITATIVE ASPECTS IN PHASE CHANGES NOTE:  When materials with small specific heat value absorbs energy, its temperature rises rapidly.  In contrast, materials with high specific heat values absorb a large amount of heat without much increase in temperature.  Water has a specific heat capacity of 4.16 Joules.
  • 60. QUANTITATIVE ASPECTS IN PHASE CHANGES SAMPLE PROBLEM:  Hot water at 100oC can burn and damage the skin, but the effect of steam on the skin can be even more severe. Calculate the amount of heat absorbed by the skin from a 150-g steam burned at 100oC.
  • 61. ENERGY CHANGES IN CHEMICAL REACTIONS Thermochemistry
  • 62. THERMOCHEMISTRY INTRODUCTION Energy is the foundation of the universe.
  • 63. THERMOCHEMISTRY  Energy transfer may be in the form of heat or work.  HEAT (Q) – is the transfer or energy between a system and surroundings due to temperature difference.  Heat may be absorbed or released by a system depending on which has a higher temperature between the system and the surroundings.
  • 64. THERMOCHEMISTRY  During chemical reaction, there is an energy change between molecules.  TWO TYPES OF REACTIONS: Endothermic Exothermic
  • 65. THERMOCHEMISTRY THERMOCHEMISTRY  The study of energy changes that occur during chemical reactions and changes of state.
  • 66. THERMOCHEMISTRY ANALYSIS  How does energy undergo change within a system or within a chemical reaction? Heat flows in and out of the system during chemical reactions.
  • 67. THERMOCHEMISTRY THE LAW OF CONSERVATION OF ENERGY:  In any chemical or physical process, energy is neither created nor destroyed.  In any chemical or physical process, energy in the universe remains unchanged. Energyuniv = constant
  • 68. THERMOCHEMISTRY Recitation: Explain how energy is conserved in the following situations:  Burning of gasoline  Hydroelectric powerplant  Cellphone telecommunications  Condensation of water vapor  Induction cooking
  • 69. THERMOCHEMISTRY THREE TYPES OF SYSTEMS: Open System Closed System Isolated System
  • 70. THERMOCHEMISTRY OPEN SYSTEM  Matter and energy occurs between system and surrounding  System interacts with the surrounding
  • 71. THERMOCHEMISTRY CLOSED SYSTEM  Only energy can transfer between system and surroundings ISOLATED SYSTEM  Matter and energy cannot transfer between the system and its surroundings.  Example: contents of adiabatic bomb calorimeter.
  • 72.
  • 73. THERMOCHEMISTRY The magnitude of heat can be computed using the following equation Q = mc T Q= heat m= mass c= specific heat capacity T= change in temperature
  • 74. THERMOCHEMISTRY WORK (w)  Force applied over a given distance  Energy transfer between a system and the surrounding due to a force acting through a distance
  • 75.
  • 76. THERMOCHEMISTRY TABLE 3.2: Assigned Convention for Work, w System does work on the surroundings -w Expansion Surroundings does work on the system +w Compression
  • 77. THERMOCHEMISTRY SAMPLE PROBLEM:  How much work is needed in a system to expand from 25 to 50 liters against a pressure of 5 atm? Is work done by the system or on the system?
  • 78. THERMOCHEMISTRY SAMPLE PROBLEM:  How much work is needed in a system to compress a carbon dioxide gas inside a fire extinguisher from the volume of 500 liter to 275 liter at 3.5 atm? Is work done by the system or on the sytem?
  • 79. THERMOCHEMISTRY ENTHALPY  In a chemical reaction, there is an energy change from the beginning up to the end of the reaction.  Change in energy: ENDOTHERMIC OR EXOTHERMIC REACTION  Represented by H
  • 80. THERMOCHEMISTRY ENTHALPY  Energy change in the reaction or the sum of all the energy stored in the bonds of the product minus the energy stored in the bond of the reactant  If there is more energy in the product than the reactant, the value of H is positive = ENDOTHERMIC REACTION
  • 81. THERMOCHEMISTRY THERMOCHEMICAL EQUATIONS  If there is less energy in the product than the reactant, the value of H is negative = EXOTHERMIC REACTION
  • 82. THERMOCHEMISTRY WRITING THERMOCHEMICAL EQUATIONS: I. When heat is lost, the H value is negative. (Exothermic reaction) CH4(g) + 2O2 ------ CO2(g) + 2H2O(l) H = -890 kJ
  • 83. THERMOCHEMISTRY WRITING THERMOCHEMICAL EQUATIONS: I. When heat is gained, the H value is positive. (Endothermic reaction) CO2(g) + 2H2O(l) ------ CH4(g) + 2O2 H = 890 kJ
  • 84. THERMOCHEMISTRY WRITING THERMOCHEMICAL EQUATIONS: II. HEAT IS A STATE FUNCTION, thus energy changes or H value for the same equation may be different if it occurs in different physical state.
  • 85. THERMOCHEMISTRY WRITING THERMOCHEMICAL EQUATIONS: III. If a reaction is reversed, then the enthalpy H value will also be reversed. Hence +a becomes –a and vice versa
  • 86. THERMOCHEMISTRY WRITING THERMOCHEMICAL EQUATIONS: III. If we change the stoichiometric coefficients in the reaction, we also change the enthalpy H value proportionally!
  • 87. THERMOCHEMISTRY WRITING THERMOCHEMICAL EQUATIONS: a. If coefficient is doubled enthalpy must be doubled also b. If we triple the coefficient, enthalpy must also be tripled c. Same with when we half the coefficient. d. If we double the equation and reverse, we must also double the enthalpy and reverse the sign
  • 88. THERMOCHEMISTRY Sample Problem: a. Manipulate the thermochemical equation below as endothermic reaction: CH4(g) + 2O2 ------ CO2(g) + 2H2O(l) H = -890 kJ
  • 89. THERMOCHEMISTRY HESS LAW  States that the enthalpy change of an overall reaction is the sum of the enthalpy changes of its individual steps. EXAMPLE: we can burn carbon directly to carbon dioxide C(s) + O2(g) ------------ CO2(g) H= -393.509 kJ OR
  • 90. THERMOCHEMISTRY HESS LAW  Carbon to carbon monoxide, then carbon monoxide to carbon dioxide C(s) + ½ O2(g) ----------- CO(G) H= -110.524 kJ CO(g) + ½ O2(g) --------- CO2(g) H= -282.958 kJ ____________________________________________ C(s) + O2(g) ------------- CO2(g) H= -393.509 kJ
  • 91. THERMOCHEMISTRY STEPS IN GETTING THE HEAT SUMMATION: 1. Identify the net equation whose ∆H is unknown. Make sure that the reaction is balanced. 2. Manipulate the equations where ∆H is known so that the correct moles of the reactants and the products are on correct sides.
  • 92. THERMOCHEMISTRY STEPS IN GETTING THE HEAT SUMMATION: 1. Add these individual reactions to get the net reaction. The value of the unknown ∆H is the sum of the individual manipulated ∆H.
  • 93. THERMOCHEMISTRY STEPS IN GETTING THE HEAT SUMMATION: 1. Add these individual reactions to get the net reaction. The value of the unknown ∆H is the sum of the individual manipulated ∆H.
  • 95. Chemical Kinetics Reaction Rate  How fast the reaction takes place  Some reactions proceed at very fast rate while others proceed very slowly  Fractions of the reactants are changed into product until all the substances are converted fully. (R)Rate= M(molar mass)/s(second)
  • 96. Examples of Reaction  Burning of Rocket Fuel  Spoiling of food outside the refrigerator  Rusting of Iron Chemical Kinetics
  • 97. Factors Affecting Rates of Reactions A. Nature of Reactants:  Reaction depends on the particular reactants and the number of bonds that have to be broken.  Reactions are rapid between oppositely- charged particles  Reactions involving covalent substances are slow at room temperature.  Gasses proceed quick reactions than solid and liquid.  The reactions between heterogeneous reactions are slower than homogeneous reactions
  • 98. Factors Affecting Rates of Reactions B. Concentration:  An increase in concentration of the reactant indirectly means an increase in collision theory, thus increasing the reaction rate.
  • 99. Factors Affecting Rates of Reactions C. Surface Area:  The smaller the size of particles, the larger the surface area exposed. A larger surface area increases the frequency of collisions
  • 100. Factors Affecting Rates of Reactions C. Effects of Catalyst:  Provides an alternative pathway of lower activation energy.  Representation of a chemical equation with the presence of catalyst: 2H2O2 → O2 + 2H2O MnO4
  • 101. Factors Affecting Rates of Reactions C. Effects of Temperature  Food spoilage at room temperature on warm summer days  Most plants grow faster in warm than in cold weather.  Animals living at moderate pressure under the deep sea are fatty than those fishes living in the shallow portion of the sea/freshwater.
  • 102. Identify the factors that influence reaction rates and explain: 1. A brush (grass fire) spreads more rapidly on a sunny day than on an overcast day. 2. Sodium reacts more rapidly with water than iron does. 3. Powdered zinc reacts more rapidly with sulfuric acid than a large piece of zinc of equal weight does. 4. It is more dangerous to drop a lighted match into a gasoline tank that has just been emptied than into one which is completely full. 5. Cake batter will cook only when heated.
  • 103. QUIZ Identify the factors that influence reaction rates and explain:
  • 105. THERMOCHEMISTRY RATE LAW  The concentration of reactants influences the rate of chemical reactions.  The effect of concentration of reactants on the rate of reaction can be seen quantitatively using the rate law for the reaction.  An expression that gives a mathematical relationship of the rate of a reaction and the concentration of reactants. Rate= k[A]m[B]n
  • 106. THERMOCHEMISTRY Consider the equation between oxygen and nitric oxide in the formation of acid rain: O2(g) + 2NO(g) → 2NO2(g) Rate= k[O2]m[NO]n
  • 107. THERMOCHEMISTRY Rate= k[O2]m[NO]n  Brackets represent the concentration of the reactants given in moles per liter  k= the fixed value for rate constant  m and n represent the order of the reaction  In getting the experimental value for m and n, the concentration of one of the reactants is changed while the other is kept constant.
  • 108. THERMOCHEMISTRY  Doubling the initial concentration of the reactants, the rate of the reaction is also doubled The reaction is FIRST ORDER WITH RESPECT TO N2O5
  • 113.
  • 114.
  • 115. Rate of Chemical Reaction The following data were obtained for the reaction: A2 + B2 +3C → D Experiment No. Reactant Concentrations Rate of Reaction (M/s) [A] [B] [C] 1 0.10 0.20 0.20 0.0090 2 0.20 0.20 0.30 0.0360 3 0.20 0.60 0.30 0.0720 4 0.20 0.20 0.60 0.2880
  • 116. BALANCING REDOX REACTIONS Review:  Electrons makes it possible for one atom bind with another atom.  In acid-base reactions, transfer of proton (H+) is involved.
  • 117. BALANCING REDOX REACTIONS What is a REDOX reaction?  RED(Reduction): Substance gain an electron  Antoine Lavosier may leave or goes in into a substance, thus changing its mass.  OX(Oxidation): Tendency of a substance to loose an electron.
  • 118. BALANCING REDOX REACTIONS REDOX IN NATURE:  Cellular Respiration  Photosynthesis  Battery charging  Burning process
  • 119. BALANCING REDOX REACTIONS In electron transfer,  We track electrons like a banking transactions. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) Fe(s) + Cu2+ (aq) + SO4 2- (aq) → Fe2+ (aq) + SO4 2- (aq) + Cu(s) Fe(s) + Cu2+ (aq) → Fe2+ (aq) + Cu(s) Lost of e- (oxidized) Gain of e- (reduced) Reducing Agent Oxidizing Agent
  • 120. BALANCING REDOX REACTIONS Oxidation number in tracking electrons:  Hypothetical value for each atom in a molecule (not actual)  ELEMENT: zero (0) oxidation# (He, O2, Fe)  MONOATOMIC ION: the same with its ionic charge (Oxygen -2, Fe +2)  NEUTRAL MOLECULE: ox. Numbers add up to get zero [CO2 (+4 -4)]
  • 121. BALANCING REDOX REACTIONS Assigning Oxidation Number: 4Fe(s) + 3O2 → 2Fe2O3 0 0 +3 -2 Fe: 0 → +3: Loss of –e [oxidized] O: 0 → -2: Gain of –e [reduced] Oxidizing Agent Reducing Agent
  • 123. BALANCING REDOX REACTIONS Balancing a Redox Reaction 0 0 +3 -2 Fe: 0 → +3: Loss of –e [oxidized] O: 0 → -2: Gain of –e [reduced] Oxidizing Agent Reducing Agent
  • 124. BALANCING REDOX REACTIONS Consider the aqueous solution iron (II) ion (Fe3+) with dichromate ion (Cr2O7 -2): 4Fe2+ + Cr2O7 -2 → 4Fe3+ Cr3+ STEPS: Separate the unbalanced reaction into half-reactions. A half reaction is an oxidation/reduction that occurs as part of overall redox reaction. Oxidation: Fe2+ → Fe3+ Reduction: Cr2O7 -2 → Cr3+
  • 125. BALANCING REDOX REACTIONS 4Fe2+ + Cr2O7 -2 → 4Fe3+ Cr3+ STEPS: Balance each of the half-reactions with regard to atoms other than O and H. In this case, no change is required for the oxidation half-reaction. We adjust the coefficient of the chromium (III) ion to balance the reduction half reaction. Oxidation: Fe2+ → Fe3+ Reduction: Cr2O7 -2 → 2Cr3+
  • 126. BALANCING REDOX REACTIONS 4Fe2+ + Cr2O7 -2 → 4Fe3+ Cr3+ STEPS: Balance both half-reactions for H by adding H+ . Once again, the oxidation in this case requires no change, but we must add 14 hydrogen ions to the product side of the reaction. Oxidation: Fe2+ → Fe3+ Reduction: Cr2O7 -2 → 2Cr3+ + 7H2O
  • 127. BALANCING REDOX REACTIONS 4Fe2+ + Cr2O7 -2 → 4Fe3+ Cr3+ STEPS: Balance both half-reactions for H by adding H+ Once again, the oxidation in this case requires no change but we must add 14 hydrogen ions to the reactant side of the reaction Oxidation: Fe2+ → Fe3+ Reduction: 14H+ + Cr2O7 -2 → 2Cr3+ + 7H2O
  • 128. BALANCING REDOX REACTIONS 4Fe2+ + Cr2O7 -2 → 4Fe3+ Cr3+ STEPS: Balance both half-reactions for charge by adding electrons. To do this, we determine the total charge on each side and add electrons to make total charges equal. Oxidation: Fe2+ → Fe3+ + e- +2 +2
  • 129. BALANCING REDOX REACTIONS 4Fe2+ + Cr2O7 -2 → 4Fe3+ Cr3+ STEPS: In case of reduction, there is total charge of [(14)(+1) + (2)(-)] = +12 on the reactant side and a total charge of [(2)(+3)] = +6 on the product side. Adding six electrons to the reactant side makes the charges equal Reduction: + 14H+ + Cr2O7 -2 → 2Cr3+ + 7H2O +6 +6 6e-
  • 130. BALANCING REDOX REACTIONS 4Fe2+ + Cr2O7 -2 → 4Fe3+ Cr3+ STEPS: If the number of electrons in the balanced oxidation half-reaction is not the same as the number of electrons in the balanced reduction half-reaction, multiply one or both of the half-reactions by the number(s) req. to make it balanced. Oxidation: 6(Fe2+ → Fe3+ e-) 6Fe2+ → 6Fe3+ 6e- Reduction: 6e- +14H+ + Cr2O7 -2 → 2Cr3+ + 7H2O
  • 131. BALANCING REDOX REACTIONS 4Fe2+ + Cr2O7 -2 → 4Fe3+ Cr3+ STEPS: Finally, add the balanced half-reactions back together and cancel the electrons, in addition to any other identical terms that appear on both sides. 6Fe2+ → 6Fe3+ 6e- 6e- +14H+ + Cr2O7 -2 → 2Cr3+ + 7H2O 6Fe2++14H+ + Cr2O7 -2 → 6Fe3+ + 2Cr3+ + 7H2O

Editor's Notes

  1. Toothpaste is still liquid but is viscous.
  2. Toothpaste is still liquid but is viscous.
  3. Toothpaste is still liquid but is viscous.
  4. Toothpaste is still liquid but is viscous.
  5. Toothpaste is still liquid but is viscous.
  6. Toothpaste is still liquid but is viscous.
  7. Observable also in graduated cylinder with liquid in it
  8. Observable also in graduated cylinder with liquid in it
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  21. Observable also in graduated cylinder with liquid in it
  22. Observable also in graduated cylinder with liquid in it
  23. Observable also in graduated cylinder with liquid in it
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  25. Observable also in graduated cylinder with liquid in it
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  27. Observable also in graduated cylinder with liquid in it
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  30. Observable also in graduated cylinder with liquid in it
  31. Observable also in graduated cylinder with liquid in it
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  34. Observable also in graduated cylinder with liquid in it
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  37. Observable also in graduated cylinder with liquid in it
  38. Observable also in graduated cylinder with liquid in it
  39. Observable also in graduated cylinder with liquid in it
  40. Heat flows from higher to lower temperature.
  41. Every substance has a certain amount of energy stored in the chemical bonds of a substance. System.
  42. System surrounding Energy(sys) + Energy (sur) = constant
  43. Example of chemical reaction
  44. Relate with love life
  45. Relate with love life
  46. Relate with love life
  47. Work can be done by the system or done on a system
  48. Work can be done by the system or done on a system
  49. Work can be done by the system or done on a system
  50. Work can be done by the system or done on a system
  51. Relate with love life
  52. Relate with love life
  53. Relate with love life
  54. Relate with love life
  55. Relate with love life
  56. Relate with love life
  57. Relate with love life
  58. Relate with love life
  59. Relate with love life
  60. Relate with love life
  61. Relate with love life
  62. Relate with love life
  63. Relate with love life
  64. Relate with love life
  65. Relate with love life
  66. Relate with love life
  67. Relate with love life
  68. Relate with love life
  69. Relate with love life
  70. Relate with love life
  71. Relate with love life
  72. Relate with love life
  73. Relate with love life
  74. Relate with love life
  75. Relate with love life
  76. Relate with love life
  77. Relate with love life
  78. Relate with love life
  79. Relate with love life
  80. Relate with love life
  81. Relate with love life
  82. Relate with love life
  83. Relate with love life
  84. Relate with love life
  85. Relate with love life
  86. Relate with love life
  87. Relate with love life
  88. Relate with love life
  89. Relate with love life
  90. Relate with love life
  91. Relate with love life
  92. Relate with love life
  93. Relate with love life
  94. Relate with love life
  95. Relate with love life